The present invention relates to a wind turbine yaw stabilizer.
Free-yawing wind turbines align with the wind aerodynamically. This is accomplished by either a tail vane, if the rotor is upwind of the tower, or an equalizing drag on the rotor if it is downwind of the tower. A characteristic of free-yawing wind turbines is that the turbine may oscillate several times about its vertical pivot axis when the wind direction changes before pointing into the wind again. Furthermore, turbulence or vertical wind shear may cause the turbine to be positioned off-line relative to the wind vector and remain thus misaligned for a period of time.
An adverse effect of the aforedescribed misalignment is a reduction in the efficiency of the rotor. Another adverse effect of the misalignment is an increase in aerodynamic loading of the rotor due to off-axis winds. Still another adverse effect is the inducing of gyroscopic loads in the rotor and drive train when the machine changes direction about its pivot axis.
U.S. Pat. No. 262,000, Chamberlain; U.S. Pat. No. 264,862, Coffield; U.S. Pat. No. 264,930, Conradson; U.S. Pat. No. 275,140, Carman; U.S. Pat. No. 293,836, Winger; U.S. Pat. No. 295,084, Underwood; U.S. Pat. No. 349,197, Albee; U.S. Pat. No. 390,698, Nichols; and U.S. Pat. No. 4,075,500, Oman et al disclose wind turbines or machines with the rotor, or "windwheel" geared to a torque shaft running down the tower to machinery on the ground; that is "power machines" as contrasted to "pumping machines." The problem dealt with is that of the torque reaction tending to turn the wind turbine partialy out of the wind, resulting in reduced efficiency, or in extreme instances, ninety degrees to the wind, ending up with shutdown. The problem seemed to be aggravated in downwind, tail-less machines, all of these patents could apply to either downwind or upwind turbines or machines.
In all these patents, except Conradson, the treatment consists in ratcheting the wind machine on the tower so as to be free to yaw in the direction opposite to that induced by the torque reaction, but locked against that tendency until there is an actual wind shift in that direction, at which time a vane activated by the new wind direction lifts the ratchet pawl and allows the turbine to assume the new, proper alignment.
Chamberlain, U.S. Pat. No. 262,000, discloses the mounting of a wind machine or turbine on a tower with a ratchet arrangement, so that it is restrained against torque reaction, but free to yaw in the other direction. A wind change in the direction of the torque reaction activates a vane, causing a pawl to lift until the machine attains alignment with the new wind direction.
Coffield, U.S. Pat. No. 264,862, discloses a device which functions on a similar principle to Chamberlain. Coffield differs in that, instead of lifting the pawl, the vane releases a brake bearing on a wheel containing the ratchet.
Conradson, U.S. Pat. No. 264,930, discloses an interrupted, active, positive drive to maintain alignment with the wind. A takeoff from the rotor shaft is directed by a vane to engage the inner or outer row of teeth on a tower-mounted bull gear to yaw the machine in either direction as required. When no motion is required, the continuously turning gear powered from the rotor shaft hovers between the two rows of gear teeth. Conradson does not mention vane damping or the amount of dead-band. The sound of a spur gear, turning at rotor speed, constantly engaging, disengaging and re-engaging would really be interesting to hear. However, it would only last for a little while.
The wind machine of Conradson is locked against torque reaction by two sets of three miter gears. Within the machine, one miter gear drives an upper and lower similar gear on vertical counter rotating shafts. These shafts, in turn, drive a tower-mounted counter shaft. The machine is thus locked against the torque reaction and cannot, in fact, move in yaw until driven by the mechanism, or aerodynamic loads, at which time a ratchet in either the upper or lower machine mounted miter gear, depending on the yaw direction required, is overridden.
Carman, U.S. Pat. No. 275,140 discloses a device which is essentially that of Chamberlain, differing only in minute detail.
Winger, U.S. Pat. No. 293,836, discloses the ratcheting of a miter gear-holding member to the tower. The independently mounted rotor is coupled through a flexible coupling or a chain drive. The rotor portion is free to track the wind within a set yaw range. Wind direction changes approaching the limits will either nudge the gear-bearing part and override the ratchet if in one direction, or lift the pawl for the other. Since the range limits are set by the capabilities of the coupling or chain arrangement, the plus or minus 45.degree. seems unrealistic.
Underwood, U.S. Pat. No. 295,084, discloses another variation on the theme of a vane controlled ratchet pawl release. Underwood adds a ground accessible hand release which is coupled with a manual feather.
Albee, U.S. Pat. No. 349,197, discloses a ratchet and pawl release and adds a ground accessible pawl release incorporated with a manual feather.
Nichols, U.S. Pat. No. 390,698, discloses essentially the same device as Chamberlain, Carman and Albee, except that the ratchet plate is spring-mounted.
Oman et al discloses a rotatable duct having an outlet to inlet area ratio greater than one. A wind-rotatable turbine is mounted within the duct. A generator driven by the turbine is a synchronous generator loading the drive from the turbine. A stator varies the incidence of wind for rotating the turbine. The stator includes a fixed leading portion and a trailing edge flap movable relative to the fixed leading portion. The trailing edge flap is movable by means sensitive to wind velocity to vary the swirl imparted to flow thereby providing a good working load distribution to all radial, span, stations of the turbine in optimizing disk loading for the turbine and the duct thereabout, so that with the load on the drive by the generator, constant turbine speed control can be effectuated over a wide range of wind velocities.
The principal object of the invention is to provide a wind turbine yaw stabilizer which eliminates the adverse effects caused by misalignment of the wind tur- bine.
An object of the invention is to provide a wind turbine yaw stabilizer which eliminates misalignment of the wind turbine.
Still another object of the invention is to provide a wind turbine yaw stabilizer which maintains the wind turbine in alignment with the wind vector.
Yet another object of the invention is to provide a wind turbine yaw stabilizer which eliminates horizontal oscillations of the turbine.
Another object of the invention is to provide a wind turbine yaw stabilizer which reduces yaw excursions and yaw rates of the wind turbine.
Still another object of the invention is to provide a wind turbine yaw stabilizer which prevents a reduction in the efficiency of the rotor, prevents an increase in aerodynamic loading of the rotor due to off-axis winds and prevents inducing of gyroscopic loads in the rotor and drive train.